1. Field of the Invention
The present invention relates to a cavity substrate having a plurality of substrates laminated thereon, and a method of manufacturing the cavity substrate.
2. Description of the Related Art
A cavity substrate B manufactured by a conventional manufacturing method is described with reference to FIG. 3.
The cavity substrate B includes a first substrate 30, a second substrate 31, and a third substrate 32. The first substrate 30 is in a square frame shape having an opening 33 in a middle part thereof. The second substrate 31 and the third substrate 32 are square flat plates. The first, second, and third substrates 30, 31, and 32 have the same external dimension. The external dimension indicates at least one, preferably both of longitudinal and lateral lengths of an outer periphery of each of the first, second, and third substrates 30, 31, and 32 during lamination.
In the cavity substrate B, the second substrate 31 and the third substrate 32 are respectively laminated on upper and lower surfaces of the first substrate 30. The opening 33 is closed from above and from below. A connection between the first substrate 30 and the second substrate 31 and a connection between the first substrate 30 and the third substrate 32 are established by interposing an adhesive layer S therebetween. A cavity K is formed using the opening 33 closed by the second and third substrates 31 and 32.
A conductor layer 34 is disposed on the upper and lower surfaces of each of the first, second, and third substrates 30, 31, and 32. The conductor layers 34 on the upper and lower surfaces of each of the substrates 30, 31, and 32 are connected to each other by a through conductor 34a extending into the substrates 30, 31, and 32.
A solder resist layer 35 is disposed on the upper surface of the second substrate 31 and on the lower surface of the third substrate 32. The solder resist layer 35 lying on the upper surface of the second substrate 31 has an opening 35a to expose a part of the conductor layer 34 lying on the upper surface of the second substrate 31. The conductor layer 34 being exposed from the opening 35a forms an electronic component connection pad 36. An electronic component is to be connected to the electronic component connection pad 36 with solder interposed therebetween.
The solder resist layer 35 lying on the lower surface of the third substrate 32 has an opening 35b to expose a part of the conductor layer 34 lying on the lower surface of the third substrate 32. The conductor layer 34 being exposed from the opening 35b forms an external connection pad 37. A wiring conductor of an external circuit board is to be connected to the external connection pad 37 with solder interposed therebetween. This establishes an electrical connection between the electronic component and the external circuit board.
A method of manufacturing the conventional cavity substrate B is described below with reference to FIGS. 4A to 4C. The same components as those in FIG. 3 have the same reference numerals, and their respective detailed descriptions are omitted.
A first step of the method is to prepare the first substrate 30, the second substrate 31, and the third substrate 32 as shown in FIG. 4A.
The substrate 30 has a thickness of approximately 0.1-0.4 mm. Each of the substrates 31 and 32 has a thickness of approximately 0.4-2.0 mm.
A second step of the method is to laminate the first substrate 30 on the third substrate 32 with an adhesive layer S interposed therebetween, thereby closing a lower side of the opening 33 as shown in FIG. 4B.
A third step of the method is to laminate the second substrate 31 on the first substrate 30 with the adhesive layer S interposed therebetween, thereby closing an upper side of the opening 33 as shown in FIG. 4C. A final step of the method is to form the cavity substrate B as shown in FIG. 3 by forming the through conductor 34a extending through each of the substrates 30, 31, and 32.
In recent years, electronic devices represented by portable communication devices and music players have become more downsized and sophisticated. Therefore, cavity substrates to be mounted on these electronic devices have been also needed to become downsized and sophisticated.
For example, a method of manufacturing an electronic component mounting substrate has been proposed by Japanese Unexamined Patent Publication No. H7-142823. The method includes preparing a workpiece shaped body with a plurality of substrates each having a circuit pattern and an electronic component mounting part, cutting the workpiece shaped body into individual piece substrates, and adhering a frame that is also used as a resin sealing frame for connecting between the individual piece substrates, to a surface-side surface of each of the individual piece substrates.
As the degrees of sophistication of the electronic devices increase, a large number of electronic elements, such as antenna elements and capacitors, are apt to be accommodated in a cavity. It is therefore necessary to ensure a certain degree of dimension of the cavity in order to accommodate the large number of electronic elements therein.
Hence, to achieve the downsizing of the cavity substrate, for example, it is necessary to increase an opening dimension of the opening 33 while reducing the external dimension of the first substrate 30.
However, a width of each of sides of the first substrate 30 which surround the opening 33 becomes extremely narrow with increasing the opening dimension of the opening 33. When the width of each side of the first substrate 30 becomes extremely narrow, a thickness of the first substrate 30 becomes extremely small, approximately 0.1-0.4 mm. A combination of both may cause significant strength degradation of the first substrate 30. Therefore, the first substrate 30 is susceptible to deformation and fracture in manufacturing processes of the cavity substrate.
Consequently, there remains the problem that it is difficult to efficiently manufacture the cavity substrate B.